Bathroom fan....do we need to replace it? Is it working at all?

14 years ago

Hi,

We are having some issues with our bathroom fan, and I wondered if someone might be able to offer some suggestions/guidance.

We have a Panasonic fan/light combo (WhisperLite, or something like that?) that was installed two years ago. If I remember correctly, it's 110CFM, which our electrician deemed the right size for our roughly 6'x10'x9'h bathroom. We did the venting ourselves, which was likely a mistake---it is a straight shot out to a roof cap (single-story house) so no big turns, but does use flex duct which I know is not the best option.

From the beginning, we had trouble with steam continuing to build up on the mirror, but the fan did seem to help somewhat. It's on a timer and typically there are two back-to-back showers totaling 20-30 minutes, and then the fan runs for another 20 minutes afterwards.

However, a few months ago we started noticing mildew on the walls. This seems like a HUGE red flag that something is amiss with the fan---we checked it and also removed the plastic grate which did have some dust build up, but it has not improved at all. Typically it takes 10-15 minutes after the last shower for the mirror and window to "unsteam" which doesn't seem normal to me, but my partner thinks this is just how fans work. We have never lived anywhere with a fan before, though, and thus neither of us really has any idea what "normal" is.

So I'm wondering....is the problem just our venting? Is it the fan, which isn't all that old? Something else altogether? The placement of the fan isn't great, and in retrospect we'd do it differently---it's centered in the room because of the light, but the shower is against one wall---but the room is so small that it didn't seem like a big deal at the time. Is it worth the cost of moving it?

We have been washing down the walls and do plan to repaint the whole room with mildew-resistant paint (not what's there now) and possibly change the tile (needs to be done anyway, and would allow us to go all the way up the wall, where the worst mildew is)---but I want to make sure we've gotten to the root of the underlying problem, too.

Any thoughts would be wonderful---just not sure what our next steps should be! Thanks!

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Comments (5)

jacobse
14 years ago
I'm no expert on these things, but 10-15 minutes to unsteam the glass sounds a bit long for me -- my soon to be remodeled bathrooms have no venting at all and the mirrors clear in that length of time!

From your questions, the first thing I think you want to determine is whether the fan is really pulling air out of the room when it's on. If you take a sheet of paper and hold it near the vent, does it get sucked up and held tight to the vent? Alternatively, if you create some smoke in the room (a cigarette, or lighting and blowing out a candle several times), can you see the smoke being pulled up and out?

Flexible duct isn't necessarily a problem; in fact some of the exhaust fan manufacturers recommend flex duct. If there are not a lot of turns, and no sharp bends, that wouldn't seem to be your problem -- unless something got in through the roof cap and is partially blocking the duct.

-- Eric
wa8b
14 years ago
For a bathroom of your size, a 110 cfm fan should be sufficient, providing it's actually exhausting 70 to 80 cfm.

A part of your problem could be that the flex ducting is causing an increase in static pressure, which reduces the ability of the fan to move air. Changing the flex to smooth metal ducting might improve the fan's performance.

You don't mention the type of roofjack or termination you have on the roof. Does it allow the exhaust stream to exit unimpeded? Does it have a back-draft flap? If so, is the flap opening properly? If it's stuck or doesn't open properly, that could be the source of your problem. Barring that, is the roofjack sized properly? If it's too small it could be constricting the air flow, which also increases static pressure, further reducing the efficiency of the fan.

If you want to read a bit more about properly sizing a bathroom exhaust system, I recommend the Fantech website. It contains a great deal of good information for properly sizing and installing an effective bath exhaust system (be sure to check out the downloadable PDF files). The information you'll find there would apply in any setting, regardless of the exhaust fan brand you're considering or have installed.

That being said, I have Fantech bath exhaust systems in all of my bathrooms. Not only do they operate in almost total silence, they are extremely effective. I never have a build-up of steam in my bathrooms, regardless of how hot or how long showers or baths go on. I haven't had a foggy bathroom mirror or condensation on windows in years.

Here is a link that might be useful: Fantech Bathroom Ventilation
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artemis78
Original Author
14 years ago
Thanks! The roof jack is a low profile roof jack cap made of metal---not sure of brand but we chose it and its size based on directions that were included with the fan, I think. I want to say it's four inches but I know it was sized to match the fan vent and ducting.

I'll try testing the draw and also will doublecheck the roof cap for anything blocking it or for flaps that aren't opening---we looked earlier in the year to make sure it was clear and it was at that point, but it's pretty accessible so worth monitoring to be sure, it sounds like.

As far as fan positioning, is that likely to make much of a difference in a bathroom this size? (In retrospect we think we should have put the fan directly over the shower, but as it is it's only a foot or so away---not sure that actually makes much difference or is worth moving....)

Thanks!
wa8b
14 years ago
The position of the exhaust fan in a bathroom the size of yours shouldn't make much difference. I don't know if it would have helped positioning the fan over the shower, but probably not. Not all fans with lights are appropriate for positioning over a shower or bath, anyway. It depends on what sort of lens is shielding the lamp. I'd guess it's not worth trying to move it.

While you're up on the roof, check to see how much air is being expelled while the fan is on. That'll be your best indication of whether it's moving a sufficient volume of air. You should feel a fairly strong blast of moving air.
jacobse
14 years ago
Wa8b wrote: A part of your problem could be that the flex ducting is causing an increase in static pressure, which reduces the ability of the fan to move air. Changing the flex to smooth metal ducting might improve the fan's performance.

Like wa8b, I recently purchased Fantech fans for our two bathroom remodels now underway. I'll just note that Fantech specifically recommends using insulated flexible ductwork, saying that it helps allow sound from the fan to dissipate gradually. You might want to check Panasonic's web site for their ducting recommendations, but assuming you used an appropriate diameter duct and length of run to the roof, I can't believe the lack of air movement you're reporting is due to using flex duct; there has to be some other culprit.

-- Eric

Bathroom fan....do we need to replace it? Is it working at all?

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Bathroom fan....do we need to replace it? Is it working at all?

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